Micromirror device

ABSTRACT

There is provided a micromirror device, which is provided with a mirror layer including a mirror surface which is supported to be rotatable around a first axis passing through a center of the mirror surface, and an upper substrate having transparency including a first upper electrode part and a second upper electrode part arranged on its surface facing the mirror layer to face each other via a first upper boundary passing through a center of the surface and parallel to the first axis, and a lower substrate including a first lower electrode part and a second lower electrode part arranged on its surface facing the mirror layer to face each other via a first lower boundary passing through a center of the surface and parallel to the first axis. The upper substrate is stacked on one side of the mirror layer while securing a first space between the center of the mirror surface and the first and second upper electrode parts, while the lower substrate is stacked on the other side of the mirror layer while securing a second space between the center of the mirror surface and the first and second lower electrode parts. The mirror surface is rotated around the first axis by applying voltage to a pair of the electrodes placed diagonally with respect to the first axis.

This is a divisional application of U.S. patent application Ser. No.11/036,983, filed Jan. 19, 2005, now U.S. Pat. No. 7,042,621, thecontents of which are expressly incorporated by reference herein in itsentirety.

BACKGROUND OF THE INVENTION

The present invention relates to a micromirror device of a capacitancetype which is used for scanning an optical beam.

Micromirror devices of the capacitance type (hereinafter also referredto simply as “micromirror devices”) have widely been used in varioustechnical fields like optical switches for communication, measuringinstruments, scanners, etc. In a micromirror device of the capacitancetype, a plurality of electrodes are arranged on a substrate which isplaced under a mirror scanning an incident beam. By applying voltage toa proper electrode, electrostatic attraction is caused between theelectrode and the mirror and thereby the surface of the mirror is tiltedin a desired direction. A typical micromirror device has been disclosedin Japanese Patent Provisional Publication No. 2003-29172 (hereinafterreferred to as a “document No. 1”), for example.

In recent years, micromirror devices are being required to secure a widescan range while achieving miniaturization. To realize a wide scanrange, some approaches for increasing the electrostatic attraction fortilting the mirror (enlarging the areas of the electrodes arranged underthe mirror, increasing the voltage applied to the electrodes, etc.) canbe taken, for example.

However, to realize the miniaturization of the whole device, there is alimit to the enlargement of the areas of electrodes. There is also alimit to the increase of the voltage applied to the electrodes since theload on the mirror surface and ill effects on other elements around themicromirror device increase. Therefore, neither approach is effectivefor practical use.

Meanwhile, a micromirror device disclosed in Japanese Patent ProvisionalPublication No. 2003-57575 (hereinafter referred to as a “document No.2”) aims to miniaturize the whole device and achieves a wide scan rangeby increasing the electrostatic attraction applied to the mirror byreducing a space between a mirror and electrodes.

SUMMARY OF THE INVENTION

However, if the space between the mirror and the electrodes is designedsmall as above, a so-called “pull-in” (the tilted mirror sticking to anelectrode and getting uncontrollable) might occur. Consequently, thecontrollable tilt angle becomes small as a matter of course and therebythe scan range is necessitated to be small.

In micromirror devices, a prescribed bias voltage is generally appliedto every electrode, that is, certain electrostatic force already existsbetween the mirror and each electrode before the device is driven forthe scanning of the beam. Therefore, if the space between the mirror andthe electrodes is reduced as above, even small electrostatic forcecorresponding to the bias voltage can pull the mirror surface toward theelectrodes. If the whole mirror surface is pulled toward the electrodes,that is, if the mirror surface moves parallelly toward the electrodes,an incident position of the beam incident upon the mirror surface shiftsfrom an original position. In such a state, the beam scans positionsdifferent from designed scanning positions.

In consideration of the above mentioned problem, the device disclosed inthe document No. 2 is provided with a pivot (a projection as asupporting point) for supporting the mirror at its center, on thesubstrate on which the electrodes are arranged, by which the translation(parallel movement) of the mirror surface toward the electrodes isavoided. Further, the micromirror device of the document No. 2 employs asubstrate having a special step-like configuration in order to preventthe aforementioned pull-in. However, a process for forming such astep-like configuration and pivot on a substrate of the small-sizedmicromirror device requires extremely high accuracy and high cost.Further, high-precision positioning for placing the pivot at the centerof the mirror becomes essential.

The present invention is advantageous in that it provides a micromirrordevice configured to have a wide scan range while being small-sized andto be manufactured with ease and at a low cost.

In accordance with an aspect of the present invention, there is provideda micromirror device, which is provided with a mirror layer including amirror surface which is supported to be rotatable around a first axispassing through a center of the mirror surface, and an upper substratehaving transparency including a first upper electrode and a second upperelectrode arranged on its surface facing the mirror layer to face eachother via a first upper boundary passing through a center of the surfaceand parallel to the first axis, and a lower substrate including a firstlower electrode and a second lower electrode arranged on its surfacefacing the mirror layer to face each other via a first lower boundarypassing through a center of the surface and parallel to the first axis.The upper substrate is stacked on one side of the mirror layer whilesecuring a first space between the center of the mirror surface and thefirst and second upper electrodes, while the lower substrate is stackedon the other side of the mirror layer while securing a second spacebetween the center of the mirror surface and the first and second lowerelectrodes. The mirror surface is rotated around the first axis byapplying voltage to a pair of electrodes, of the first and second upperelectrodes and the first and second lower electrodes, placed diagonallywith respect to the first axis.

As above, the micromirror device of the present invention employs theelectrodes arranged above and below the mirror surface, in which thenumber of electrodes used for the rotation of the mirror surface isdoubled, that is, effective electrode area for the rotation of themirror surface is doubled compared to conventional micromirror devices,by which a large tilt angle of the mirror surface can be achieved. Inthe micromirror device of the present invention, the aforementionedpull-in is avoided while ensuring the large tilt angle, by securing asufficient space between the mirror surface and the electrodes of eachsubstrate. Since the effective electrode area is enlarged as above, awide scan range can be attained even if the voltage applied to eachelectrode is reduced to a low level.

In conventional micromirror devices, the mirror surface is rotated onlyby electrostatic attraction occurring between the mirror surface and anelectrode placed on one side of the mirror surface. In other words, themirror is rotated only by linear pulling force applied to one side ofthe mirror, by which the structure of the mirror layer is subject todamages caused by a heavy load. Meanwhile, in the present invention, themirror surface is rotated around the first axis by applying voltage to apair of electrodes placed diagonally with respect to the first axis. Inthe operation, both sides of the mirror surface is pulled upward anddownward respectively, by which a substantially pure bending moment(rotation moment) can be given to the mirror surface efficiently. Thestructure of the mirror layer is released from a heavy load and therebya longer operating life can be attained.

Further, in the above composition, the bias voltage is applied to boththe upper and lower electrodes. Therefore, the displacement of themirror surface can be avoided efficiently without the need of forming asupporting part like the pivot of the document No. 2.

As described above, the micromirror device of the present inventionachieves a wide scan range while maintaining a small-sized and simpleconfiguration even though the thickness slightly increases by that ofthe upper substrate.

Optionally, the pair of electrodes placed diagonally with respect to thefirst axis may be in a symmetrical relationship with respect to thecenter of the mirror surface. By such configuration, the voltage controlof the electrodes becomes easier.

Still optionally, the mirror surface may be supported to be furtherrotatable at least around a second axis intersecting with the first axisat the center. In this case, the upper substrate further includes athird upper electrode and a fourth upper electrode arranged on thesurface facing the mirror layer to face each other via a second upperboundary passing through the center of the surface and parallel to thesecond axis. The lower substrate further includes a third lowerelectrode and a fourth lower electrode arranged on the surface facingthe mirror layer to face each other via a second lower boundary passingthrough the center of the surface and parallel to the second axis. Themirror surface can be rotated around the second axis by applying voltageto a pair of electrodes, of the third and fourth upper electrodes andthe third and fourth lower electrodes, placed diagonally with respect tothe second axis.

Still optionally, the pair of electrodes placed diagonally with respectto the second axis may be in a symmetrical relationship with respect tothe center of the mirror surface, similarly to the pair of electrodesplaced diagonally with respect to the first axis.

In the case of biaxial mirror rotation (i.e. two-dimensional scanning ofthe beam incident upon the mirror surface), by configuring themicromirror device to let the first and second axes intersect with eachother at right angles, the control of mirror rotation can be simplifiedand facilitated.

In the case of the biaxial mirror rotation, the mirror, layer mayinclude a frame provided around the mirror surface, an outer frameprovided around the frame, first hinge parts arranged along the firstaxis to connect the mirror surface and the frame, and second hinge partsarranged along the second axis to connect the frame with the outerframe.

Still optionally, the first and second spaces may be formed to havesubstantially the same heights. Especially when all the electrodesprovided to the upper and lower substrates are in a symmetricalrelationship with respect to the mirror surface, the equalization of theheights of the first and second spaces facilitates the voltage controlsince the voltages to be applied to the electrodes placed diagonallywith respect to the rotation axis for the rotation of the mirror surfacecan be set substantially equal to each other.

Still optionally, the micromirror device is provided with a first spacerfor forming the first space, and a second spacer for forming the secondspace.

When spacers for securing the first and second spaces are providedbetween the mirror layer and the upper and lower substrates, one of thespacers can be formed integrally with the mirror layer. Such compositionallows the spacer to be formed simultaneously with the manufacture ofthe mirror layer by etching, etc., by which the manufacturing process ofthe whole micromirror device can be simplified.

While the tilt angle of the mirror surface can be increased by enlargingthe electrodes as mentioned above, too large electrode area on the uppersubstrate causes blockage of the incident beam by the electrodes. In aparticular case, the electrodes provided to the upper substrate may beformed as transparent electrodes.

In a particular case, the electrodes of the upper substrate may beplaced at positions avoiding blockage of optical paths of the beambefore being incident upon the mirror surface and after being deflectedby the mirror surface. For example, the electrodes of the uppersubstrate may be arranged to form an annular shape letting the beamenter the central part of the upper substrate.

Incidentally, the manufacturing process of the micromirror device can befurther simplified by giving compatibility to the substrates of thedevice. Therefore, it is preferable that the electrodes provided to thelower substrate be configured substantially the same as the electrodesof the upper substrate.

According to another aspect of the invention, there is provided ascanning confocal probe, which is provided with the micromirror devicedescribed above, a single mode optical fiber which guides the beamemitted from the light source while guiding the beam reflected by thetissue to a photoreceptor unit, a deflector which deflects the beamemerging from the single mode optical fiber toward the micromirrordevice, and a mounting substrate having transparency which is used forinstalling the micromirror device and the deflector along an opticalpath of the beam. The micromirror device and the deflector are mountedon opposite sides of the mounting substrate.

In such a scanning confocal probe to be inserted in a body cavity, thevoltage applied to each electrode is desired to be set as low aspossible. The micromirror device of the present invention is capable ofachieving a wide scan range while reducing the voltage applied to eachelectrode to a low level as mentioned above. Therefore, the scanningconfocal probe in accordance with the present invention realizesobservation of a wide range while ensuring the safety.

It is also possible to utilize the upper substrate of the micromirrordevice as the aforementioned mounting substrate. Specifically, the uppersubstrate is designed larger (longer) than the mirror layer and thelower substrate, and the deflector is placed on a surface of the uppersubstrate opposite to the mirror layer. By such composition, relativepositions of the micromirror device, the deflector and the single modeoptical fiber forming the scanning confocal probe can be set easily.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

FIG. 1 is a perspective view showing the overall composition of amicromirror device in accordance with an embodiment of the presentinvention;

FIG. 2 is a perspective view showing components of the micromirrordevice in a disassembled state;

FIG. 3 is a schematic diagram showing the cross-sectional configurationof a mirror layer of the micromirror device along an X axis;

FIG. 4A is a cross-sectional view of an upper substrate of themicromirror device taken along the line A—A shown in FIG. 2;

FIG. 4B is a bottom view of the upper substrate seen from the mirrorlayer's side;

FIG. 4C is a top view of the upper substrate seen from the lightincident side;

FIG. 5A is a cross-sectional view of the micromirror device taken alonga plane containing the X axis and the line A—A of FIG. 2, showing thestatus of the device before the application of voltage to driveelectrodes;

FIG. 5B is a cross-sectional view of the micromirror device taken alonga plane containing the X axis and the line A—A of FIG. 2, showing thestatus of the device with a prescribed voltage applied to driveelectrodes; and

FIG. 6 is a schematic diagram showing the basic composition of ascanning confocal probe equipped with the micromirror device of theembodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Referring now to the drawings, a description will be given in detail ofa preferred embodiment in accordance with the present invention. FIG. 1is a perspective view showing the overall configuration of a micromirrordevice 10 according to an embodiment of the present invention. As shownin FIG. 1, the micromirror device 10 is formed in a shape like a cuboid.FIG. 2 is a perspective view showing components of the micromirrordevice 10 in a disassembled state.

As shown in FIGS. 1 and 2, the micromirror device 10 includes an uppersubstrate 2 and a lower substrate 3 stacked up to sandwich a mirrorlayer 1. The upper substrate 2 is stacked on the mirror layer 1 via aspacer 4, and thus the micromirror device 10 includes the uppersubstrate 2, the spacer 4, the mirror layer 1 and the lower substrate 3from its light incident side. In this description, part of themicromirror device 10 in the light incident side is defined as an “upperpart” and the other part is defined as a “lower part” for the sake ofconvenience.

As shown in FIG. 2, the mirror layer 1 includes a circular mirrorsurface 11 placed in the central part of the mirror layer 1, aring-shaped frame 12 placed to surround the periphery of the mirrorsurface 11, and an outer frame 13 formed to surround the frame 12. Theframe 12 has a pair of hinge parts 12X arranged in a first direction (xdirection) to sandwich the mirror surface 11 (hereinafter referred to as“first hinge parts 12X”). Each first hinge part 12X is joined to themirror surface 11 at one end, while being joined to the frame 12 at theother end. Therefore, the first hinge parts 12X support the mirrorsurface 11 to be rotatable around an X axis in the x direction. Theframe 12 is further provided with another pair of hinge parts 12Yarranged in a second direction (y direction) orthogonal to the xdirection to sandwich the frame 12 (hereinafter referred to as “secondhinge parts 12Y”). Each second hinge part 12Y is joined to the frame 12at one end, while being connected to the outer frame 13 at the otherend. Therefore, the second hinge parts 12Y support the frame 12 and themirror surface 11 to be rotatable around a Y axis in the y direction. InFIG. 2, the X and Y axes are indicated with broken lines and theintersection of the two axes (the center of the mirror surface 11) isindicated with a reference character “C1”.

The structure of the first and second hinge parts 12X and 12Y is notparticularly limited. For example, a thin material alternately folded indirections orthogonal to each axis may be employed in this embodiment aseach hinge part.

FIG. 3 is a schematic diagram showing the cross-sectional configurationof the mirror layer 1 shown in FIG. 2 along the X axis. As shown in FIG.3, a protruded part 14 is provided to a peripheral part of the outerframe 13 facing the lower substrate 3 so as to protrude downward by aprescribed level difference compared with the central part where themirror surface 11 is placed. The protruded part 14 is formed in order tosecure a prescribed space (hereinafter referred to as a “lower space”)between the mirror layer 1 and the lower substrate 3.

The mirror layer 1 configured as above is manufactured by processing anSOI (Silicon On Insulator) wafer by dry etching like RIE (Reactive IonEtching) or various wet etching techniques. Specifically, the SOI waferis composed of three layers: an active or device layer (Si), a box layer(SiO₂) and a handle layer (Si). By vapor-depositing a metal layer (Al,Au, etc.) or dielectric multiple layers on the surface of the activelayer processed as shown in FIG. 3 by RIE, the mirror layer 1 having themirror surface 11 of high reflectivity is obtained.

Next, the upper substrate 2 will be explained referring to FIGS. 4Athrough 4C. FIG. 4A is a cross-sectional view of the upper substrate 2shown in FIG. 2 taken along the line A—A (diagonal line). FIG. 4B is abottom view of the upper substrate 2 seen from the mirror layer's side.FIG. 4C is a top view of the upper substrate 2 seen from the lightincident side.

The upper substrate 2 is prepared by processing a glass substrate 2 ahaving sufficient transparency allowing a beam led from outside to beincident upon the mirror surface 11. As shown in FIGS. 4A and 4B, firstthrough fourth drive electrodes T1–T4 are formed on a plane surface 2 bof the upper substrate 2 facing the mirror layer 1. Each drive electrodeT1–T4 is formed as a transparent electrode like an ITO(Indium-Tin-Oxide) film so as not to block the incidence of the beamupon the mirror surface 11. The drive electrodes T1–T4 are shaped intosector forms of the same size. Specifically, first and second driveelectrodes T1 and T2 are placed to be symmetrical with each other withrespect to a boundary passing through the center C2 of the uppersubstrate 2 and stretching in the y direction (first boundary,corresponding to the Y axis of the mirror layer 1). Third and fourthdrive electrodes T3 and T4 are placed to be symmetrical with each otherwith respect to a boundary passing through the center C2 and stretchingin the x direction (second boundary, corresponding to the X axis of themirror layer 1).

As shown in FIGS. 4A and 4C, on a surface 2 c of the upper substrate 2opposite to the surface 2 b facing the mirror layer 1, first throughfourth wiring electrodes t1–t4 are formed so that voltage supplied fromthe outside of the micromirror device 10 can be applied to the driveelectrodes T1–T4.

The glass substrate 2 a is also provided with conducting parts 2 d forelectrically connecting the wiring electrodes t1–t4 to the driveelectrodes T1–T4, respectively. Each conducting part 2 d is formed byopening a through hole through the glass substrate 2 a by sand blasting,etc. and filling the through hole with conductive material. Theformation of the conducting part 2 d (through hole) by sand blasting isonly an example, and thus other techniques can also be used as long asthe conducting part 2 d (through hole) can be formed. By the aboveconfiguraton, voltage supplied from the outside of the micromirrordevice 10 can be applied to the drive electrodes T1–T4 via theconducting parts 2 d.

The lower substrate 3 in this embodiment is configured to be the same asthe upper substrate 2 which has been described above. By the common useof the same substrate configuration for the upper and lower substrates 2and 3, costs can be reduced and efficiency of assembly work can beincreased. Further, among the electrodes facing one another via themirror layer 1 (mirror surface 11), those placed diagonally with respectto the X axis or the Y axis are in symmetrical relationship with eachother with respect to the center C1 of the mirror surface 11. Therefore,the electrostatic forces produced when a predetermined voltage isapplied to the electrodes become substantially the same.

The spacer 4 is provided in order to secure a prescribed space(hereinafter referred to as an “upper space”) between the uppersubstrate 2 and the mirror layer 1. Specifically, the spacer 4 is madeof silicon to have substantially the same height as the protruded part14 of the mirror layer 1. In other words, in the micromirror device 10of this embodiment, the upper space secured by the spacer 4 hassubstantially the same height as the lower space secured by theprotruded part 14. Therefore, electrostatic forces applied to the mirrorsurface 11 when a certain voltage is applied to the electrodes T1 to T4become substantially the same, and thus application of bias voltagecauses no displacement of the mirror surface 11.

In the stacking of the components 1 to 4, various joining techniques canbe used. In this embodiment, the components 1 to 4 are joined togetherby anode junction. Since the spacer 4 and the mirror layer 1 (both madeof silicon) can not be joined directly by anode junction, a thin glasslayer is placed between the spacer 4 and the mirror layer 1 and the twolayers are joined together by anode junction via the glass layer.Incidentally, an error in the height of the upper space caused by theglass layer has no effect in practical use since the glass layer is farthinner than each component 1–4.

In cases where the components 1–4 are vacuum-packaged in the last stepof the manufacturing process of the micromirror device 10, the use of aspacer 4 made of Pyrex glass is desirable. Parts that can not be joinedtogether by anode junction may also be joined by use of polyimideadhesives like Photoneece.

The principle of operation of the micromirror device 10 configured asabove will be explained below referring to FIGS. 5A and 5B. The mirrorlayer 1 shown in FIGS. 5A and 5B has the same configuration as thatshown in FIG. 3. Thus, FIGS. 5A and 5B are cross-sectional views of themicromirror device 10 taken along a plane containing the X axis and theline A—A shown in FIG. 2, in which FIG. 5A shows the status of themicromirror device 10 before the application of voltage to drive theelectrodes and FIG. 5B shows the status of the micromirror device 10with a prescribed voltage applied to drive electrodes. In FIGS. 5A and5B, for discriminating between the drive electrodes T1–T4 provided tothe upper substrate 2 and the lower substrate 3, drive electrodes of theupper substrate 2 are referred to as “upper drive electrodes T1 u–T4 u”while those of the lower substrate 3 are referred to as “lower driveelectrodes T1 d–T4 d” for the sake of convenience.

To rotate the mirror surface 11 around the Y axis, a prescribed voltage(+V) is applied to a lower drive electrode T1 d and an upper driveelectrodes T2 u as shown in FIG. 5A. By the application of the voltage,electrostatic force (attraction) is caused between the mirror surface 11and each drive electrode T1 d, T2 u as indicated by solidly shadedarrows in FIG. 5A, by which the mirror surface 11 and the frame 12rotate around the Y axis formed by a pair of second hinge parts 12Y (seeFIG. 2) as shown in FIG. 5B. To rotate the mirror surface 11 around theY axis in a direction opposite to FIG. 5B, the prescribed voltage (+V)is applied to a lower drive electrode T2 d and an upper drive electrodesT1 u.

As above, the micromirror device 10 of this embodiment rotates themirror surface 11 (and the frame 12) around the Y axis by simultaneouslyapplying the same voltage to a pair of drive electrodes T1 d and T2 u ora pair of drive electrodes T2 d and T1 u which are placed diagonallywith respect to the Y axis. Each electrostatic force caused by theapplication of voltage is applied to the mirror surface 11 substantiallyas a pure bending moment, as indicated by solidly shaded arrows in FIG.5B. Therefore, the load on the second hinge parts 12Y and the mirrorsurface 11 in regard to the mirror rotation can be reduced compared to aconventional micromirror device.

Further, by the provision of the drive electrodes to both of the uppersubstrate 2 and the lower substrate 3, a large electrode area can beachieved for the mirror rotation. Moreover, sufficient spaces (the upperspace, the lower space) are secured by the spacer 4 and the protrudedpart 14 of the mirror layer 1. Therefore, by the micromirror device 10according to the embodiment of the present invention, a large tilt angleis secured even if the voltage applied to each electrode is reduced to alow level.

The above is the principle of operation of the micromirror device 10 ofthis embodiment. Incidentally, while only the rotation of the mirrorsurface 11 around the Y axis has been described above, the rotation ofthe mirror surface 11 around the X axis is also accomplished bysubstantially the same principle, except for the following points. Inthe rotation around the X axis, the voltage is applied to a pair ofdrive electrodes (an upper drive electrode T3 u and a lower driveelectrode T4 d, or an upper drive electrode T4 u and a lower driveelectrode T3 d) which are placed diagonally with respect to the X axis.Since the first hinge parts 12X serve as the rotation axis, the frame 12does not rotate in this case.

The micromirror device 10 described above can be used suitably as alaser beam scanning unit of a scanning confocal probe, for example. FIG.6 is a schematic diagram showing a basic configuration of a scanningconfocal probe 100 which is equipped with the micromirror device 10 ofthis embodiment.

As shown in FIG. 6, the scanning confocal probe 100 includes an opticalfiber 20, a GRIN (GRadient INdex) lens 30, a deflecting system 40 and anobjective lens 50.

The optical fiber 20 is a single mode fiber which transmits light in asingle mode. The optical fiber 20 receives an optical beam emitted by anunshown light source and guides the beam to the GRIN lens 30. The GRINlens 30 functions as a collimator lens for collimating the beam emergingfrom the optical fiber 20. The collimated beam emitted from the GRINlens 30 is incident upon the deflecting system 40.

The deflecting system 40 includes the aforementioned micromirror device10 and a mirror part (i.e. a deflector) 5 which deflects the incidentbeam to the micromirror device 10.

In conventional scanning confocal probes, the micromirror device and themirror part are manufactured separately and thereafter mounted on thescanning confocal probe while being registered with (positioned relativeto) each other via a mounting substrate having transparency. Therefore,very high accuracy is required not only in the registration of themicromirror device with the mirror part but also in optical pathmatching with other members in the mounting process. Under suchcircumstances, deterioration of manufacturing efficiency has beenpointed out.

Meanwhile, in the micromirror device 10 of this embodiment, the uppersubstrate 2 (specifically, the glass substrate 2 a) is designed to belarger than the other components 1, 3 and 4 as shown in FIG. 6, that is,the upper substrate 2 is formed to serve as the aforementioned mountingsubstrate. The mirror part 5 is formed on a surface of the uppersubstrate 2 opposite to a surface facing the mirror layer 1 (surfacenearer to the objective lens 50). By forming the deflecting system 40 asa single unit as above, the registration of the micromirror device 10with the mirror part 5 becomes unnecessary, and the optical pathmatching with other members 20, 30 and 50 in the mounting on thescanning confocal probe 100 is also facilitated.

In the deflecting system 40, the collimated beam is incident upon themirror layer 1 (specifically, the mirror surface 11) of the micromirrordevice 10 via the mirror part 5 and the upper substrate 2. Thecollimated beam reflected by the mirror layer 1 irradiates a livingtissue K in a body cavity while being converged by the objective lens50. Meanwhile, the mirror surface 11 rotates around the X axis or the Yaxis according to the aforementioned principle of operation, by whichthe living tissue K is scanned by the beam two-dimensionally.

The beam reflected by the living tissue K proceeds reversely on theabove optical path and is guided by the optical fiber 20 to aphotoreceptor. In this process, the end face of the optical fiber 20functions as a pinhole, that is, only reflected light from a focal planeof the objective lens 50 on the object side enters the optical fiber 20through the end face.

While the present invention has been described with reference to theparticular illustrative embodiment, it is not to be restricted by theembodiment but only by the appended claims. It is to be appreciated thatthose skilled in the art can change or modify the embodiment withoutdeparting from the scope and spirit of the present invention. Forexample, the following modifications can also achieve effects similar tothose of the above embodiment.

In the micromirror device 10 of the above embodiment, all the driveelectrodes provided to the upper substrate 2 and the lower substrate 3are arranged to be symmetrical with respect to the center C1 of themirror surface 11 from the viewpoint of easy voltage control. Further,the upper space and the lower space are designed to have equal heightsin order to equalize electrostatic attraction applied to the mirrorsurface 11 due to application of a prescribed voltage (bias voltage) toeach electrode. However, if a controller in charge of the voltagecontrol is capable of more flexible voltage control and ill effect onthe controller is negligible, the shape and size of each electrode, theheight of each space, etc. can be designed to be different. In thiscase, effects similar to those of the above embodiment can be obtainedby letting the controller change the voltage applied to each electrodein accordance with the shape and size of each electrode, the height ofeach space, etc. It is also possible to compensate for individualdifferences (manufacturing error, etc.) of the electrodes by theadjustment of the voltage applied to each electrode.

While a biaxial micromirror device 10 (capable of rotating the mirrorsurface 11 around two axes) has been described in the above embodimentas the most frequently used type, the micromirror device 10 according tothe present invention is not restricted to the biaxial type but can beuniaxial, triaxial, or more. While a configuration in which the two axes(X axis, Y axis) intersect at right angles has been explained above as aconfiguration allowing easiest control, the axes do not necessarily haveto be orthogonal.

While the mirror layer 1 is integrally provided with the protruded part14 for securing the lower space in the above embodiment, the way ofsecuring the space can be different. For example, the lower space may besecured by an independent spacer like the spacer 4 for the upper space,instead of forming the protruded part 14.

In the above embodiment, the electrodes on the upper substrate 2 areformed as transparent electrodes. However, if the electrodes of theupper substrate 2 are placed at positions avoiding blockage of opticalpaths of the beam before being incident upon the mirror surface 11 andafter being deflected by the mirror surface 11, the electrodes need notto be transparent. For example, the drive electrodes of the uppersubstrate 2 may be arranged to form an annular shape around the areainterfering with the optical paths.

As described above, in accordance with the present invention, theelectrodes for rotating the mirror surface are arranged both above andbelow the mirror surface, by which a micromirror device achieving alarge tilt angle of the mirror surface (i.e. a wide scan range) whileremaining small-sized can be provided. The micromirror device, requiringno special structure for preventing the displacement of the mirrorsurface, etc., can be manufactured with ease and at a low cost.

A substrate of the micromirror device of the present invention can beused as a mounting substrate of a scanning confocal probe, by whichpositioning of the micromirror device relative to other members in theprobe can be made easily.

The micromirror device according to the present invention is capable ofachieving a wide scan range even when the voltage applied to eachelectrode is low. Therefore, the micromirror device is suitable not onlyfor optical switches, measuring instruments, scanners, etc. (technicalfields where micromirror devices are currently used) but also formedical applications (the aforementioned scanning confocal probe, etc.).

The present disclosure relates to the subject matter contained inJapanese Patent Application No. P2004-012237, filed on Jan. 20, 2004,which is expressly incorporated herein by reference in its entirety.

1. A micromirror device, comprising: a mirror layer including a mirrorsurface which is supported to be rotatable around a first axis passingthrough a center of the mirror surface, the mirror layer being formedfrom a Silicon On Insulator wafer; a transparent upper substrate havinga first upper electrode and a second upper electrode arranged on asurface of the upper substrate facing the mirror layer, the first andsecond upper electrodes comprising sectors of an upper generallycircular electrode pattern, the first upper electrode beingsymmetrically arranged with respect to the second upper electrode acrossa first upper boundary passing through a center of the upper substratesurface parallel to the first axis, the upper substrate being stacked onone side of the mirror layer while securing a first space between thecenter of the mirror surface and the first and second upper electrodes;and a lower substrate having a first lower electrode and a second lowerelectrode arranged on a surface of the lower substrate facing the mirrorlayer, the first and second lower electrodes comprising sectors of alower generally circular electrode pattern, the first lower electrodebeing symmetrically arranged with respect to the second lower electrodeacross a first lower boundary passing through a center of the surfaceparallel to the first axis, the lower substrate being stacked on theother side of the mirror layer while securing a second space between thecenter of the mirror surface and the first and second lower electrodes,wherein the mirror surface is rotated around the first axis by applyingvoltage to a pair of electrodes, of the first and second upperelectrodes and the first and second lower electrodes, placed diagonallywith respect to the first axis.
 2. The micromirror device according toclaim 1, wherein the pair of electrodes placed diagonally with respectto the first axis is in a symmetrical relationship with respect to thecenter of the mirror surface.
 3. The micromirror device according toclaim 1, wherein the mirror surface is supported to be further rotatableat least around a second axis intersecting with the first axis at thecenter of the mirror surface, wherein the upper substrate furtherincludes a third upper electrode and a fourth upper electrode arrangedon the surface of the upper substrate facing the mirror layer, the thirdand fourth upper electrodes comprising sectors of the upper generallycircular electrode pattern, the third upper electrode beingsymmetrically arranged with respect to the fourth upper electrode acrossa second upper boundary passing through the center of the uppersubstrate surface and parallel to the second axis, wherein the lowersubstrate further includes a third lower electrode and a fourth lowerelectrode arranged on the surface of the lower substrate facing themirror layer, the third and fourth lower electrodes comprising sectorsof the lower generally circular electrode pattern, the third lowerelectrode being symmetrically arranged with respect to the fourth lowerelectrode across a second lower boundary passing through the center ofthe lower substrate surface and parallel to the second axis, and whereinthe mirror surface is rotated around the second axis by applying voltageto a pair of electrodes, of the third and fourth upper electrodes andthe third and fourth lower electrodes, placed diagonally with respect tothe second axis.
 4. The micromirror device according to claim 3, whereinthe pair of electrodes placed diagonally with respect to the second axisis in a symmetrical relationship with respect to the center of themirror surface.
 5. The micromirror device according to claim 3, whereinthe first and second axes intersect with each other at right angles. 6.The micromirror device according to claim 3, wherein the mirror layerincludes: a frame provided around the mirror surface; an outer frameprovided around the frame; first hinge parts arranged along the firstaxis to connect the mirror surface and the frame; and second hinge partsarranged along the second axis to connect the frame with the outerframe.
 7. The micromirror device according to claim 1, wherein the firstand second spaces are formed to have substantially the same heights. 8.The micromirror device according to claim 1, further comprising: a firstspacer that forms the first space; and a second spacer that forms thesecond space.
 9. The micromirror device according to claim 8, whereinone of the first and second spacers is integrally formed with the mirrorlayer.
 10. The micromirror device according to claim 1, wherein thefirst and second upper electrodes comprise transparent electrodes. 11.The micromirror device according to claim 1, wherein the first andsecond upper electrodes of the upper substrate are placed at positionssuch that they do not block an optical path of a beam incident upon themirror surface and do not block an optical path of a beam deflected bythe mirror surface.
 12. The micromirror device according to claim 1,wherein the sectors comprise generally quarter-circles.
 13. Amicromirror device, comprising: a mirror layer, comprising a mirrorsurface configured to rotate around two axes; an upper substrate,comprising an upper electrode pattern formed generally in the shape of acircle, the upper electrode pattern comprising a plurality of upperelectrodes, each having generally the shape of a circle quadrant; and alower substrate, comprising a lower electrode pattern formed generallyin the shape of a circle, the lower electrode pattern comprising aplurality of lower electrodes, each having generally the shape of acircle quadrant, wherein the mirror layer is provided between the upperand lower substrates, and the mirror surface is configured to rotate byapplying voltage to a pair of electrodes of the upper and lowerelectrode patterns.
 14. The micromirror device according to claim 13,wherein the mirror surface is configured to rotate in a first directionaround a first axis by applying a voltage to a first upper electrode ofthe plurality of upper electrodes and to a first lower electrode of theplurality of lower electrodes, and is configured to rotate in a seconddirection around the first axis by applying a voltage to a second upperelectrode of the plurality of upper electrodes and to a second lowerelectrode of the plurality of lower electrodes.
 15. The micromirrordevice according to claim 14, wherein the mirror surface is configuredto rotate in a third direction around a second axis by applying avoltage to a third upper electrode of the plurality of upper electrodesand to a third lower electrode of the plurality of lower electrodes, andis configured to rotate in a fourth direction around the second axis byapplying a voltage to a fourth upper electrode of the plurality of upperelectrodes and to a fourth lower electrode of the plurality of lowerelectrodes.